Detecting whether a patient has a bacterial infection is important in providing suitable treatment for the patient. Often, this detection can be difficult because of the infection's location, for example, in the lungs or gastrointestinal tract. Methods of detecting the presence of particular bacteria by measuring isotopically-labeled ratios of volatile gases have been reported. See, e.g., U.S. Pat. No. 7,717,857, U.S. Published Application No. 2012/0298868, and PCT/US2013/029626. But methods of detecting other bacteria are still needed.
Epidemic infection with the intestinal pathogen Clostridium difficile (C. diff) is becoming highly important worldwide, especially in the United States with estimates that there were 300,000 cases of C. diff. associated disease (CDAC) in 2005 with its incidence still increasing. McDonald, L. C., G. E. Killgore, A. Thompson, R. C. Owens, Jr., S. V. Kazakova, S. P. Sambol, S. Johnson, and D. N. Gerding, (2005) An epidemic, toxin gene-variant strain of Clostridium difficile, N Engl J Med. 353: 2433-2441; Zilberberg, M. D., A. F. Shorr, and M. H. Kollef, (2008) Increase in adult Clostridium difficile-related hospitalizations and case-fatality rate, United States, 2000-2005, Emerg Infect Dis. 14: 929-931.
C. diff. infection results in antibiotic-associated disease, from diarrhea to the potentially fatal pseudomembranous colitis. It is believed that when the normal bowel microflora of patients is disrupted by antibiotic treatments, this allows C. diff. to proliferate and cause disease. C. diff. is also highly transmissible in hospital or long term care facilities and may cause epidemics of infection. In addition to its ability to generate host-damaging toxins, C. diff. also can ferment p-hydrophenylacetate, generated from tyrosine, to p-cresol. This is thought to give C. diff. a competitive advantage in the gut by poisoning other species. Indeed, epidemic strains of C. diff. are efficient producers of p-cresol.
Although methods to diagnose C. diff. are available, they are not suitable for estimating bacterial load in a patient to assist in a diagnosis. Moreover, the currently available methods are not able to guide treatment. For example, attempts to use cresol detection in feces as a diagnostic failed due to sensitivity issues. The current standard for diagnosis is toxigenic culture, an expensive culture-based test that takes 48 hours for results. Carroll, K. C., Tests for the diagnosis of Clostridium difficile infection: The next generation, Anaerobe. 17: 170-174. A number of enzyme immunoassays and PCR based techniques are being developed and tested, but it is unclear whether they can become a gold standard, or whether they are of use in monitoring treatment or cure as none of these tests are quantitative.
The average cost to treat each case of CDAC in the US is presently between $9,000 and $12,000. Furthermore, the highly transmissible nature of C. diff. in hospital or long-term care facilities enables it to cause epidemics of infection, and so rapid detection and effective treatment is essential in tackling C. diff. Accordingly, novel methods and tools for diagnosing and treating C. diff. are desirable.